Pirfenidone is a small molecule with a molecular weight of 185.23 daltons whose chemical name is 5-methyl-1-phenyl-2-(1H)-pyridone. Pirfenidone has anti-fibrotic properties and has been investigated for therapeutic benefits to patients suffering from various fibrotic conditions. It is approved in Japan for treatment of idiopathic pulmonary fibrosis (IPF) under the trade name Pirespa®, and in several European countries under the trade name Esbriet®.
Pirfenidone has been shown to be metabolized by various isoforms of the cytochrome P450 (CYP) protein [See the Report on the Deliberation Results, Evaluation and Licensing Division, Pharmaceutical and Food Safety Bureau, Ministry of Health Labour and Welfare, Sep. 16, 2008]. Specifically, several cytochrome P450 (CYP) isoforms (CYP1A2, 2C9, 2C19, 2D6 and 2E1) were reported to be involved in the earliest stages of oxidative metabolism of pirfenidone. More recently, it was reported that in vitro experiments showed that pirfenidone metabolism is predominantly carried out by CYP1A2 [U.S. Pat. No. 7,816,383, incorporated by reference herein in its entirety].
Ciprofloxacin is a broad spectrum antimicrobial agent. Ciprofloxacin hydrochloride, USP, a fluoroquinolone, is the monohydrochloride monohydrate salt of 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid. It has a molecular weight of 385.8, its empirical formula is C17H18FN3O3.HCl.H2O and its chemical structure is as follows:

Ciprofloxacin was previously classified as a moderate inhibitor of CYP1A2 by the FDA [FDA Draft Guidance for Industry Drug Interaction Studies—Study Design, Data Analysis, and Implications for Dosing and Labeling, September 2006]; this description was recently revised in February 2012 [FDA Draft Guidance for Industry Drug Interaction Studies—Study Design, Data Analysis, Implications for Dosing, and Labeling Recommendations, February 2012].